The Detection of Time-Varying Crustal Properties: Diving into the Seismic Dumpster for Treasure Matthew M. Haney U.S. Geological Survey, Alaska Volcano Observatory
Why are small changes important? Changes in the Earth usually subtle and spatially limited Seismic deployments often sparse Bulk seismic velocity varies ~1% in response to tectonic and volcanic processes Small changes invisible to tomography May be the only way to seismically detect aseismic processes Monitoring for early signs of unrest
Imaging the crust with seismic noise Shapiro et al. (2005) Science Brenguier et al. (2007) GRL
Types of change detected Co- and post-seismic changes Poupinet et al. (1984) Volcanic unrest Temperature and precipitation Aseismic processes Where are we going? Imagine... it s easy if you try
Doublet method in an nutshell
One without and one with sleeves a Δa
Wrapping a short cable
Wrapping a long cable
Difference ΔL Δa/a = -ΔL/L or Δv/v = -Δt/t
Co- and post-seismic changes Coyote Lake Eq - Poupinet et al. (1984) Parkfield Eq - Brenguier et al. (2008) L Aquila Eq - Duvet et al. (2010) Tohoku Eq - Nakata and Snieder (2011) Tohoku Eq - Minato et al. (2012) Many more studies Strong shaking modifies the near-surface Healing occurs over months
Nakata and Snieder (2011) GRL
Volcanic unrest Piton de la Fournaise - Brenguier et al. (2008) Montserrat - Baptie (2010) Merapi - Poupinet and Ratdompurbo (1996) Vesuvius - Pandolfi et al. (2006) Asama - Nagaoka et al. (2010) Pavlof - Haney et al. (2009)
Brenguier et al. (2008) Nat. Geosci. Duputel et al. (2009) JVGR
Time delay in coda at Pavlof Volcano Haney et al. (2009) TLE
2009 eruption of Redoubt Volcano
Figure by S. de Angelis
Redoubt s magmatic system Grapenthin et al. (2012) JVGR
Temperature and precipitation Merapi - Sens-Schonfelder and Wegler (2006) Japan - Nakata and Snieder (2011) The Moon - Sens-Schonfelder and Larose (2008) Infrasound - Haney (2009)
Infrasound monitoring Haney (2009) GRL
Inversions occur between 1-7am Inversion 1 Inversion 2 Inversion 3 No inversion Inversion 4 No inversion Inversion 5
Aseismic processes Guerrero, Mexico - Rivet et al. (2011) Velocity changes due to Slow Slip Event (SSE) Velocity change occurred during peak strain rate Gofar Fault, EPR - McGuire et al. (2012) Velocity changes during a foreshock swarm Velocity change correlated with seismicity rate Nonlinear elasticity
McGuire et al. (2012) Nat. Geosci.
Imaging versus change detection Ambient noise tomography (ANT) susceptible to artifacts or ghosts ANT also requires a minimum offset between stations Both issues irrelevant for change detection Only stable noise sources are needed
2 stations
Derivation of traveltime change 1. v = d/t 2. v+δv = d/(t+δt) changes in v & t v+δv = d/t (dδt)/t 2 Taylor series Δv = (vδt)/t Using Eq 1. Δv/v = Δt/t Poupinet et al.
θ
Taking oblique angle into account 1. v/cosθ = d/t (v+δv)/cosθ = d/(t+δt) (v+δv)/cosθ = d/t (dδt)/t 2 1. Δv/cosθ = (vδt)/(t cosθ) Δv/v = Δt/t Same result!
... changes in the medium can be observed even if the Green's function of the medium is not reconstructed... the Green's function reconstruction in the correlations is not a necessary condition: The only condition to monitoring with correlation passive experiment is the relative stability of the background noise structure. Hadziioannou et al. (2009) JASA
Stable tremor visible in correlations Haney (2010) JGR
Dawson et al. (2010) GRL
VLP tremor at Kilauea May/June 2007 Differen$al distance to Pu u O o Sta$on distance Feb/Mar 2008 Differen$al distance to Halema uma u Ballmer, et al. (2012) In prep
Possible dirty sources Anthropogenic Traffic Machinery Drilling Active sources Stable volcanic and tectonic tremor Tremor location and characterization
Time-varying anisotropy New observable in addition to dt/t Parkfield Eq - Durand et al. (2010) Polarization direction Tohoku Eq - Nakata and Snieder (2012) 60% change in anisotropy parameter Large changes due to greater sensitivity
Future New observables besides dt/t Anisotropy changes New processes Glaciers and ice-sheets? Marsan et al. (2012) State-of-the-art networks and instruments De-emphasizing Green s functions and instead seeking stable noise sources Continued integration into monitoring
Considering a new research direction? I hope someday you ll join us...
Grand challenges addressed How do faults slip? How does the near-surface environment affect natural hazards and resources? What is the relationship between stress and strain in the lithosphere? How do processes in the ocean and atmosphere interact with the solid earth? How do magmas ascend and erupt?
Lack of seismicity prior to eruption
Time-lapse time delay time (s) time (s) Haney et al. (2009) TLE
Increasing delay during the eruption Haney et al. (2009) TLE
Figure by S. de Angelis
Figure by S. de Angelis
Figure by S. de Angelis
One (approach to volcano monitoring) is to track the volcano s changes in response to known, repeating natural signals such as earth tides. Newhall (2007) Volcanology 101 for Seismologists